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Abstract:

An electric energy storage apparatus can generate an AC output in a
low-loss and low-noise manner without using a DC-DC converter or an
inverter. The electric energy storage apparatus comprises: an electric
energy storage module group formed by connecting in series electric
energy storage modules each comprising one or more electric energy
storage elements; a balancing circuit electrically connected to the
electric energy storage module group and configured to adjust a voltage
to be applied to each of the electric energy storage modules; a first
switch group comprising switches each in a path connecting a first
terminal and a terminal of one of the series-connected electric energy
storage modules; and a second switch group comprising switches each in a
path connecting a second terminal and a terminal of one of the
series-connected electric energy storage modules. The electric energy
storage apparatus may perform a switch changeover in the switch groups.

Claims:

1. An electric energy storage apparatus comprising: an electric energy
storage module group formed by connecting in series two or more electric
energy storage modules each comprising one or more electric energy
storage elements; a balancing circuit electrically connected to the
electric energy storage module group and configured to adjust a voltage
to be applied to each of the electric energy storage modules; a switch
group comprising two or more switches each provided in a path connecting
a first connection point and a terminal of one of the series-connected
electric energy storage modules; and a positive-negative inversion
circuit having, as an input section, the first connection point and a
second connection point electrically connected to one of the terminals of
the series-connected electric energy storage modules, the
positive-negative inversion circuit being configured to connect the first
connection point and the second connection point to one of output
terminals respectively, wherein the electric energy storage apparatus is
configured to perform a switch changeover in the switch group so as to
select a magnitude of an output voltage depending on a configuration of
the electric energy storage elements present in a path connecting the
first and second connection points, and cause the positive-negative
inversion circuit to select a polarity of the output voltage depending on
the output terminals connected to respective ones of the first and second
connection points.

2. An electric energy storage apparatus comprising: an electric energy
storage module group formed by connecting in series two or more electric
energy storage modules each comprising one or more electric energy
storage elements, each of the electric energy storage modules being
connected to a DC power supply; a switch group comprising two or more
switches each provided in a path connecting a first connection point and
a terminal of one of the series-connected electric energy storage
modules; and a positive-negative inversion circuit having, as an input
section, the first connection point and a second connection point
electrically connected to one of the terminals of the series-connected
electric energy storage modules, the positive-negative inversion circuit
being configured to connect the first connection point and the second
connection point to one of output terminals respectively, wherein the
electric energy storage apparatus is configured to perform a switch
changeover in the switch group so as to select a magnitude of an output
voltage depending on a configuration of the electric energy storage
elements present in a path connecting the first and second connection
points, and cause the positive-negative inversion circuit to select a
polarity of the output voltage depending on the output terminals
connected to respective ones of the first and second connection points.

3. The electric energy storage apparatus as defined in claim 1, which
further comprises: voltage detection means configured to detect a voltage
across the electric energy storage module; first switch-group control
means configured to, based on the electric energy storage module voltage
detected by the voltage detection means, and a voltage magnitude in a
target output voltage waveform at a certain clock time, turn on one of
the switches comprised in the switch group; and positive-negative
inversion circuit control means configured to, based on a voltage
polarity in the target output voltage waveform at the certain clock time,
select the output terminals to be connected to the first connection point
and the second connection point, in the positive-negative inversion
circuit, wherein the electric energy storage apparatus is configured to,
depending on the magnitude and polarity of the target output voltage
waveform, and the electric energy storage module voltage, control the
switch group and the positive-negative inversion circuit to output a
voltage having the target output voltage waveform.

4. The electric energy storage apparatus as defined in claim 1, which
further comprises: voltage detection means configured to detect a voltage
across a load connected to the output terminals; first switch-group
control means configured to, based on the load voltage detected by the
voltage detection means, and a voltage magnitude in a target output
voltage waveform at a certain clock time, turn on one of the switches
comprised in the switch group; and positive-negative inversion circuit
control means configured to, based on a voltage polarity in the target
output voltage waveform at the certain clock time, select the output
terminals to be connected to the first connection point and the second
connection point, in the positive-negative inversion circuit, wherein the
electric energy storage apparatus is configured to, depending on the
magnitude and polarity of the target output voltage waveform, and the
load voltage, control the switch group and the positive-negative
inversion circuit to output a voltage having the target output voltage
waveform.

5. The electric energy storage apparatus as defined in claim 1, which
further comprises: load voltage detection means configured to detect a
voltage across a load connected to the output terminals; and second
switch-group control means configured to, based on a voltage in the
target output voltage waveform at a certain clock time, and a load
voltage detected at the certain clock time by the load voltage detection
means, turn on one of the switches comprised in the switch group, wherein
the electric energy storage apparatus is configured to adjust the load
voltage to conform to the voltage in the target output voltage waveform
at the certain clock time, by charging and discharging between the load
and the electric energy storage module connected to the load through the
switch turned on by the second switch-group control means.

6. A method of outputting a voltage using the electric energy storage
apparatus as defined in claim 1, comprising the steps of: inputting a
reference waveform signal from reference waveform outputting means; based
on the reference waveform signal, determining a voltage magnitude and
polarity in a target output voltage waveform at a certain clock time;
based on the electric energy storage module voltage, and the voltage
magnitude in the target output voltage waveform at the certain clock
time, turning on one of the switches comprised in the switch group; and
based on the voltage polarity in the target output voltage waveform at
the certain clock time, selectively connecting each of the first
connection point and the second connection point to one of the output
terminals, in the positive-negative inversion circuit, wherein a
magnitude and polarity of the output voltage are selected at intervals of
a predetermined period of time to adjust the output voltage to conform to
the target output voltage waveform.

7. The method as defined in claim 6, which comprises a step of performing
a switchover among at least two states selected from the group consisting
of a state in which all of the switches in the switch group are turned
off and all of states in which any one of the switches in the switch
group is turned on, once or more within the predetermined period of time,
to adjust a temporal average value of the output voltage within the
predetermined period of time.

8. An electric energy storage apparatus comprising: an electric energy
storage module group formed by connecting in series two or more electric
energy storage modules each comprising one or more electric energy
storage elements; a balancing circuit electrically connected to the
electric energy storage module group and configured to adjust a voltage
to be applied to each of the electric energy storage modules; a first
switch group comprising two or more switches each provided in a path
connecting a first terminal and a terminal of one of the series-connected
electric energy storage modules; and a second switch group comprising two
or more switches each provided in a path connecting a second terminal and
a terminal of one of the series-connected electric energy storage
modules, wherein the electric energy storage apparatus is configured to
perform a switch changeover in the first and second switch groups so as
to select a magnitude and polarity of an output voltage depending on a
configuration of the electric energy storage elements present in a path
connecting the first and second terminals.

9. An electric energy storage apparatus comprising: an electric energy
storage module group formed by connecting in series two or more electric
energy storage modules each comprising one or more electric energy
storage elements, each of the electric energy storage modules being
connected to a DC power supply; a first switch group comprising two or
more switches each provided in a path connecting a first terminal and a
terminal of one of the series-connected electric energy storage modules;
a second switch group comprising two or more switches each provided in a
path connecting a second terminal and a terminal of one of the
series-connected electric energy storage modules, wherein the electric
energy storage apparatus is configured to perform a switch changeover in
the first and second switch groups so as to select a magnitude and a
polarity of an output voltage depending on a configuration of the
electric energy storage elements present in a path connecting the first
and second terminals.

10. The electric energy storage apparatus as defined in claim 8, which
further comprises: voltage detection means configured to detect a voltage
across the electric energy storage module; and first switch-group control
means configured to, based on the electric energy storage module voltage
detected by the voltage detection means, and a voltage in a target output
voltage waveform at a certain clock time, turn on one of the switches
comprised in a respective one of the first and second switch groups,
wherein the electric energy storage apparatus is configured to, depending
on a magnitude and polarity of the target output voltage waveform, and
the electric energy storage module voltage, control the first and second
switch groups to output a voltage having the target output voltage
waveform.

11. The electric energy storage apparatus as defined in claim 8, which
further comprises: voltage detection means configured to detect a voltage
across a load connected to the electric energy storage apparatus; and
first switch-group control means configured to, based on the load voltage
detected by the voltage detection means, and a voltage in a target output
voltage waveform at a certain clock time, turn on one of the switches
comprised in a respective one of the first and second switch groups,
wherein the electric energy storage apparatus is configured to, depending
on a magnitude and polarity of the target output voltage waveform, and
the load voltage, control the first and second switch groups to output a
voltage having the target output voltage waveform.

12. The electric energy storage apparatus as defined in claim 8, which
further comprises: load voltage detection means configured to detect a
voltage across a load connected to the electric energy storage apparatus;
and second switch-group control means configured to, based on a voltage
in the target output voltage waveform at a certain clock time, and a load
voltage detected at the certain clock time by the load voltage detection
means, turn on one of the switches comprised in a respective one of the
first and second switch groups, wherein the electric energy storage
apparatus is configured to adjust the load voltage to conform to the
voltage in the target output voltage waveform at the certain clock time,
by charging and discharging between the load and the electric energy
storage module connected to the load through the switches turned on by
the second switch-group control means.

13. A method of outputting a voltage using the electric energy storage
apparatus as defined in claim 8, comprising the steps of: inputting a
reference waveform signal from reference waveform outputting means; based
on the reference waveform signal, determining a voltage magnitude and
polarity in a target output voltage waveform at a certain clock time; and
based on the electric energy storage module voltage, and the voltage
magnitude and polarity in the target output voltage waveform at the
certain clock time, turning on one of the switches comprised in a
respective one of the first and second switch groups, wherein a magnitude
and polarity of the output voltage are selected at intervals of a
predetermined period of time to adjust the output voltage to conform to
the target output voltage waveform.

14. The method as defined in claim 13, which comprises a step of
performing a switchover among at least two states selected from the group
consisting of a state in which all of the switches in the first or second
switch group are turned off and all of states in which any one of the
switches in a respective one of the first and second switch groups is
turned on, once or more within the predetermined period of time to adjust
a temporal average value of the output voltage within the predetermined
period of time.

15. The electric energy storage apparatus as defined in claim 1, wherein
at least one of the one or more electric energy storage elements is a
capacitor or a secondary battery.

Description:

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application is a continuation of International Patent
Application No. PCT/JP2010/063697 filed on Aug. 12, 2010, which claims
priority from Japanese Patent Application No. 2009-202633 filed on Sep.
2, 2009, all of which are hereby incorporated by reference in their
entirety for all purposes.

FIELD

[0002] The present invention relates to an electric energy storage
apparatus. More specifically, the present invention relates to an
electric energy storage apparatus capable of generating an AC output in a
low-loss and low-noise manner without using a DC (direct current)-DC
converter and an inverter.

BACKGROUND

[0003] As one example of a power supply for generating an AC (alternating
current) voltage, there is a type based on a system designed to convert a
voltage held by electric energy storage means such as a capacitor,
through a DC-DC converter and an inverter.

[0004]FIG. 1 illustrates a typical circuit configuration of such an AC
power supply. This electric energy storage apparatus comprises: electric
energy storage means; a discharge circuit; a DC/DC converter; and an
inverter.

[0005] Generally, when a certain electronic device is operated by electric
power, it is necessary to supply electric power within a predetermined
operating voltage range which is determined by characteristics of the
device. This is because, although an electronic device can adequately
operate within a predetermined voltage range depending on individual
characteristics of the device, it becomes operationally unstable or
becomes non-operative if a supply voltage changes to a value out of the
operating voltage range. Therefore, in the above AC power supply, it is
essential to perform control for allowing an output voltage therefrom to
fall within a certain range, primarily based on the DC-DC converter.

[0006] Patent Document 1: JP 2008-219964 A

[0007] Patent Document 2: JP H06-225462 A

[0008] Patent Document 3: JP S54-126931 A

[0009] Patent Document 4: U.S. Pat. No. 3,100,851 B

[0010] Patent Document 5: JP 2007-166691 A

[0011] Patent Document 6: JP H07-115728 A

[0012] Patent Document 7: JP 2002-345157 A

SUMMARY

[0013] According to an aspect of the present invention, there is provided
an electric energy storage apparatus which comprises: an electric energy
storage module group formed by connecting in series two or more electric
energy storage modules each comprising one or more electric energy
storage elements; a balancing circuit electrically connected to the
electric energy storage module group and configured to adjust a voltage
to be applied to each of the electric energy storage modules; a switch
group comprising two or more switches each provided in a path connecting
a first connection point and a terminal of one of the series-connected
electric energy storage modules; a positive-negative inversion circuit
having, as an input section, the first connection point and a second
connection point electrically connected to one of the terminals of the
series-connected electric energy storage modules, wherein the
positive-negative inversion circuit is configured to connect the first
connection point and the second connection point to one of output
terminals, respectively; electric energy storage module voltage detection
means configured to detect a voltage across the electric energy storage
module; switch group control means configured to, based on the electric
energy storage module voltage detected by the electric energy storage
module voltage detection means, and a voltage magnitude in a target
output voltage waveform at a certain clock time, turn on one of the
switches comprised in the switch group; and positive-negative inversion
circuit control means configured to, based on a voltage polarity in the
target output voltage waveform at the certain clock time, select the
output terminals to be connected to the first connection point and the
second connection point, in the positive-negative inversion circuit,
wherein the electric energy storage apparatus is configured to, depending
on the magnitude and polarity of the target output voltage waveform, and
the electric energy storage module voltage, perform a switch changeover
in the switch group, and a selection of the output terminals to be
connected to the first and second connection points in the
positive-negative inversion circuit, so as to select a magnitude of an
output voltage depending on a configuration of the electric energy
storage elements present in a path connecting the first and second
connection points, and select a polarity of the output voltage depending
on the output terminals connected to respective ones of the first and
second connection points, to output a voltage having the target output
voltage waveform.

[0014] The above electric energy storage apparatus is configured to select
a magnitude of the output voltage by the switch changeover in the switch
group, and is free of the need for a conventional DC-DC converter using a
coil or a transformer. A voltage generated from the electric energy
storage module group to have a desired magnitude selected by the switch
changeover is subjected to polarity (positive-negative) conversion by the
positive-negative inversion circuit according to need, and then output
through the output terminals.

[0015] In the above electric energy storage apparatus, a voltage across
each of the electric energy storage modules is adjusted by the balancing
circuit, so that it is possible to adjust the output voltage in
increments of the adjusted voltage.

[0016] In cases where an element having a large voltage change, such as a
capacitor, is used as the electric energy storage element, it is
desirable to monitor a temporally-changing voltage by the electric energy
storage module voltage detection means. This is because, even when one of
the switches is fixedly turned on, a capacitor voltage will be gradually
lowered due to discharging, so that it is necessary to frequently perform
the switch changeover so as to obtain an output voltage within an
operating range. The electric energy storage module voltage detection
means may be any suitable device configured to measure a voltage and
output an analog or digital signal depending on the measured voltage.

[0017] In one aspect, preferably, the switch changeover depending on a
voltage change in the electric energy storage element and a target
voltage is performed by the switch group control means. In cases where a
semiconductor switch, such as a MOSFET, is used as each of the switch,
the switch group control means may be any switch driver composed, for
example, of an RF oscillation circuit.

[0018] As one example of the switch driver, it is possible to use a
programmable switch driver configured to compare the electric energy
storage module voltage detected by the electric energy storage module
voltage detection means with a voltage of the target waveform, to
determine an optimal switch changeover state, and then generate a
changeover signal to the switch group. However, it is not essential for
the switch group control means to have the above configuration. For
example, the comparison operation may be performed by any suitable
comparison and calculation circuit. Further, it is not essential that the
electric energy storage module voltage detection means and the switch
group control means are formed as individual separate means, but they may
be formed as a single device having their functions.

[0019] The above electric energy storage apparatus configured to adjust an
output voltage to conform to a target voltage at a certain clock time
makes it possible to adjust the output voltage at intervals of a
predetermined period of time to output a voltage in an arbitrary pattern,
regardless of whether it is a DC voltage or an AC voltage.

[0020] In addition, according to an aspect of the present invention, there
is provided an electric energy storage apparatus which comprises: an
electric energy storage module group formed by connecting in series two
or more electric energy storage modules each comprising one or more
electric energy storage elements; a balancing circuit electrically
connected to the electric energy storage module group and configured to
adjust a voltage to be applied to each of the electric energy storage
modules; a switch group comprising two or more switches each provided in
a path connecting a first connection point and a terminal of one of the
series-connected electric energy storage modules; and a positive-negative
inversion circuit having, as an input section, the first connection point
and a second connection point electrically connected to one of the
terminals of the series-connected electric energy storage modules,
wherein the positive-negative inversion circuit is configured to connect
the first connection point and the second connection point to one of
output terminals, respectively, and wherein the electric energy storage
apparatus is configured to perform a switch changeover in the switch
group so as to select a magnitude of an output voltage depending on a
configuration of the electric energy storage elements present in a path
connecting the first and second connection points, and cause the
positive-negative inversion circuit to select a polarity of the output
voltage depending on the output terminals connected to respective ones of
the first and second connection points.

[0021] As each of the aforementioned control means, it is possible to use
any external device. In this case, the external devices may be
appropriately connected to the above electric energy storage apparatus in
use. The object of the present invention can also be achieved in this
manner.

[0022] In addition, according to an aspect of the present invention, there
is provided an electric energy storage apparatus which comprises: an
electric energy storage module group formed by connecting in series two
or more electric energy storage modules each comprising one or more
electric energy storage elements, wherein each of the electric energy
storage modules is connected to a constant-voltage DC power supply; a
switch group comprising two or more switches each provided in a path
connecting a first connection point and a terminal of one of the
series-connected electric energy storage modules; and a positive-negative
inversion circuit having, as an input section, the first connection point
and a second connection point electrically connected to one of the
terminals of the series-connected electric energy storage modules,
wherein the positive-negative inversion circuit is configured to connect
the first connection point and the second connection point to one of
output terminals, respectively, and wherein the electric energy storage
apparatus is configured to perform a switch changeover in the switch
group so as to select a magnitude of an output voltage depending on a
configuration of the electric energy storage elements present in a path
connecting the first and second connection points, and cause the
positive-negative inversion circuit to select a polarity of the output
voltage depending on the output terminals connected to respective ones of
the first and second connection points.

[0023] The above electric energy storage apparatus is configured such that
a DC power supply is connected to each of the electric energy storage
modules, instead of using the balancing circuit. As one example, a
constant-voltage DC power supply may be connected to each of the electric
energy storage modules. This makes it possible to adjust the output
voltage without taking into account a voltage drop in each of the
electric energy storage modules.

[0024] The electric energy storage apparatus according to the present
invention may further comprise: voltage detection means configured to
detect a voltage across the electric energy storage module; first
switch-group control means configured to, based on the electric energy
storage module voltage detected by the voltage detection means, and a
voltage magnitude in a target output voltage waveform at a certain clock
time, turn on one of the switches comprised in the switch group; and
positive-negative inversion circuit control means configured to, based on
a voltage polarity in the target output voltage waveform at the certain
clock time, select the output terminals to be connected to the first
connection point and the second connection point, in the
positive-negative inversion circuit, wherein the electric energy storage
apparatus is configured to, depending on the magnitude and polarity of
the target output voltage waveform, and the electric energy storage
module voltage, control the switch group and the positive-negative
inversion circuit to output a voltage having the target output voltage
waveform.

[0025] Alternatively, the electric energy storage apparatus according to
an aspect of the present invention may further comprise: voltage
detection means configured to detect a voltage across a load connected to
the output terminals; first switch-group control means configured to,
based on the load voltage detected by the voltage detection means, and a
voltage magnitude in a target output voltage waveform at a certain clock
time, turn on one of the switches comprised in the switch group; and
positive-negative inversion circuit control means configured to, based on
a voltage polarity in the target output voltage waveform at the certain
clock time, select the output terminals to be connected to the first
connection point and the second connection point, in the
positive-negative inversion circuit, wherein the electric energy storage
apparatus is configured to, depending on the magnitude and polarity of
the target output voltage waveform, and the load voltage, control the
switch group and the positive-negative inversion circuit to output a
voltage having the target output voltage waveform.

[0026] The electric energy storage apparatus may be configured to directly
detect the load voltage, instead of the electric energy storage module
voltage, and adjust the output voltage based on the detected load
voltage. A specific mathematical relationship is established between the
electric energy storage module voltage and the load voltage, depending on
one of the switches to be selectively turned on. Thus, it is only
necessary to detect one of them so as to adjust an output voltage.

[0027] The electric energy storage apparatus according to an aspect of the
present invention may further comprise: load voltage detection means
configured to detect a voltage across a load connected to the output
terminals; and second switch-group control means configured to, based on
a voltage in the target output voltage waveform at a certain clock time,
and a load voltage detected at the certain clock time by the load voltage
detection means, turn on one of the switches comprised in the switch
group, wherein the electric energy storage apparatus is configured to
adjust the load voltage to conform to the voltage in the target output
voltage waveform at the certain clock time, by charging and discharging
between the load and the electric energy storage module connected to the
load through the switch turned on by the second switch-group control
means.

[0028] In cases where an AC voltage is output to a load including a
reactive element such as a coil and a capacitor (or a load having an
unignorable level of certain reactance component), the load voltage is
likely to deviate from a target voltage, due to, for example, an induced
electromotive force generated in the load. Particularly, when a high
frequency voltage having a temporal change is output, the deviation
becomes larger. Moreover, due to influence of load fluctuation, residual
potential, etc., the load voltage is likely to deviate from a target
value of the output voltage.

[0029] The above electric energy storage apparatus makes it possible to
detect an actual load voltage different from the target value, by the
load voltage detection means, and connect the load to any one of the
electric energy storage modules to directly adjust the load voltage by
means of charging and discharging. In addition, excess energy in the load
can be regeneratively returned to the electric energy storage module so
as to compensate for a voltage drop in each of the electric energy
storage modules to some extent, which leads to stabilization in
operation.

[0030] In addition, according to an aspect of the present invention, there
is provided a method of outputting a voltage using the electric energy
storage apparatus described above. The method comprises the steps of:
inputting a reference waveform signal from reference waveform outputting
means; based on the reference waveform signal, determining a voltage
magnitude and polarity in a target output voltage waveform at a certain
clock time; based on the electric energy storage module voltage, and the
voltage magnitude in the target output voltage waveform at the certain
clock time, turning on one of the switches comprised in the switch group;
and, based on the voltage polarity in the target output voltage waveform
at the certain clock time, selectively connecting each of the first
connection point and the second connection point to one of the output
terminals, in the positive-negative inversion circuit, wherein a
magnitude and polarity of the output voltage are selected at intervals of
a predetermined period of time to adjust the output voltage to conform to
the target output voltage waveform.

[0031] The aspect of the present invention provides a specific process for
outputting a voltage having a desired waveform pattern using the electric
energy storage apparatus of the present invention.

[0032] The above method may comprise a step of performing a switchover
among at least two states selected from the group consisting of a state
in which all of the switches in the switch group are turned off and all
of states in which any one of the switches in the switch group is turned
on, once or more within the predetermined period of time, to adjust a
temporal average value of the output voltage within the predetermined
period of time.

[0033] In the method described above, when a temporally-changing voltage
is output, for example, through a switch changeover at intervals of a
predetermined period of time, the switch changeover can be performed in a
plurality of states for providing different output voltages within the
predetermined period of time to further finely adjust a substantial
(temporal average) voltage within the predetermined period of time. As
one example, a changeover between a state in which all of the switches is
turned off and a state in which an integer number of series-connected
electric energy storage modules contribute to the output can be performed
at high speed to obtain an output voltage corresponding to a voltage
across a half of the integer number of series-connected electric energy
storage modules. This makes it possible to adjust the output voltage in a
multi-step manner by pulse width modulation (PWM) control, even if the
electric energy storage apparatus comprises a small number of electric
energy storage modules.

[0034] In addition, according to an aspect of the present invention, there
is provided an electric energy storage apparatus which comprises: an
electric energy storage module group formed by connecting in series two
or more electric energy storage modules each comprising one or more
electric energy storage elements; a balancing circuit electrically
connected to the electric energy storage module group and configured to
adjust a voltage to be applied to each of the electric energy storage
modules; a first switch group comprising two or more switches each
provided in a path connecting a first terminal and a terminal of one of
the series-connected electric energy storage modules; and a second switch
group comprising two or more switches each provided in a path connecting
a second terminal and a terminal of one of the series-connected electric
energy storage modules, wherein the electric energy storage apparatus is
configured to perform a switch changeover in the first and second switch
groups so as to select a magnitude and polarity of an output voltage
depending on a configuration of the electric energy storage elements
present in a path connecting the first and second terminals.

[0035] The electric energy storage apparatus described above makes it
possible to select the magnitude and polarity of the output voltage by
the switch changeover in the first and second switch groups, without
using a positive-negative inversion circuit. Typically, the polarity can
be selected by switching from which of the first and second switch groups
a switch on the higher potential side is selected and from which of the
first and second switch groups a switch on the lower potential side is
selected.

[0036] In addition, according to an aspect of the present invention, there
is provided an electric energy storage apparatus which comprises: an
electric energy storage module group formed by connecting in series two
or more electric energy storage modules each comprising one or more
electric energy storage elements, wherein each of the electric energy
storage modules is connected to a constant-voltage DC power supply; a
first switch group comprising two or more switches each provided in a
path connecting a first terminal and a terminal of one of the
series-connected electric energy storage modules; a second switch group
comprising two or more switches each provided in a path connecting a
second terminal and a terminal of one of the series-connected electric
energy storage modules, wherein the electric energy storage apparatus is
configured to perform a switch changeover in the first and second switch
groups so as to select a magnitude and a polarity of an output voltage
depending on a configuration of the electric energy storage elements
present in a path connecting the first and second terminals.

[0037] The above electric energy storage apparatus is configured such that
a constant-voltage DC power supply is connected to each of the electric
energy storage modules, instead of using the balancing circuit.

[0038] The electric energy storage apparatus according to an aspect of the
present invention may further comprise: voltage detection means
configured to detect a voltage across the electric energy storage module;
and first switch-group control means configured to, based on the electric
energy storage module voltage detected by the voltage detection means,
and a voltage in a target output voltage waveform at a certain clock
time, turn on one of the switches comprised in a respective one of the
first and second switch groups, wherein the electric energy storage
apparatus is configured to, depending on a magnitude and polarity of the
target output voltage waveform, and the electric energy storage module
voltage, control the first and second switch groups to output a voltage
having the target output voltage waveform.

[0039] Alternatively, the electric energy storage apparatus according to
an aspect of the present invention may further comprise: voltage
detection means configured to detect a voltage across a load connected to
the electric energy storage apparatus; and first switch-group control
means configured to, based on the load voltage detected by the voltage
detection means, and a voltage in a target output voltage waveform at a
certain clock time, turn on one of the switches comprised in a respective
one of the first and second switch groups, wherein the electric energy
storage apparatus is configured to, depending on a magnitude and polarity
of the target output voltage waveform, and the load voltage, control the
first and second switch groups to output a voltage having the target
output voltage waveform.

[0040] As above, the electric energy storage apparatus may be configured
to directly detect the load voltage, instead of the electric energy
storage module voltage, and adjust the output voltage based on the
detected load voltage.

[0041] The electric energy storage apparatus according to the fifth or
sixth aspect of the present invention may further comprise: load voltage
detection means configured to detect a voltage across a load connected to
the electric energy storage apparatus; and second switch-group control
means configured to, based on a voltage in the target output voltage
waveform at a certain clock time, and a load voltage detected at the
certain clock time by the load voltage detection means, turn on one of
the switches comprised in a respective one of the first and second switch
groups, wherein the electric energy storage apparatus is configured to
adjust the load voltage to conform to the voltage in the target output
voltage waveform at the certain clock time, by charging and discharging
between the load and the electric energy storage module connected to the
load through the switches turned on by the second switch-group control
means.

[0042] The above electric energy storage apparatus makes it possible to
correct a load voltage deviation due to a reactance component in the
load, and regeneratively return excess energy to the electric energy
storage module so as to compensate for a voltage drop in each of the
electric energy storage modules.

[0043] In addition, according to an aspect of the present invention, there
is provided a method of outputting a voltage using the electric energy
storage apparatus according to the fifth or sixth aspect of the present
invention. The method comprises the steps of: inputting a reference
waveform signal from reference waveform outputting means; based on the
reference waveform signal, determining a voltage magnitude and polarity
in a target output voltage waveform at a certain clock time; and based on
the electric energy storage module voltage, and the voltage magnitude and
polarity in the target output voltage waveform at the certain clock time,
turning on one of the switches comprised in a respective one of the first
and second switch groups, wherein a magnitude and polarity of the output
voltage are selected at intervals of a predetermined period of time to
adjust the output voltage to conform to the target output voltage
waveform.

[0044] The method described above provides a specific process for
outputting a voltage having a desired waveform pattern using the electric
energy storage apparatus of the present invention.

[0045] The method described above may comprises a step of performing a
switchover among at least two states selected from the group consisting
of a state in which all of the switches in the first or second switch
group are turned off and all of states in which any one of the switches
in a respective one of the first and second switch groups is turned on,
once or more within the predetermined period of time to adjust a temporal
average value of the output voltage within the predetermined period of
time.

[0046] This makes it possible to adjust the output voltage in a multi-step
manner by pulse width modulation control.

[0047] In the present invention, a capacitor or a secondary battery may be
used as the electric energy storage element. However, the electric energy
storage apparatus of the present invention may be constructed using any
other element, module, device, or the like.

[0049]FIG. 2 is a circuit diagram illustrating an AC output-capable
electric energy storage apparatus according to a first embodiment of the
present invention.

[0050]FIG. 3 is a circuit diagram illustrating a switched capacitor
usable as one example of a balancing circuit.

[0051]FIG. 4 is a graph illustrating one example of a voltage waveform to
be input into a positive-negative inversion circuit via connection points
A, B, in the electric energy storage apparatus in FIG. 2.

[0052]FIG. 5 is a diagram illustrating a switch changeover to be
performed to compensate for an influence of voltage drop in electric
energy storage modules.

[0053]FIG. 6 is a graph illustrating one example of a voltage waveform to
be applied to a load by the electric energy storage apparatus in FIG. 2.

[0054]FIG. 7 is a circuit diagram illustrating an AC output-capable
electric energy storage apparatus according to a second embodiment of the
present invention.

[0055] FIG. 8a is a graph illustrating one example of an output voltage
waveform obtained when a switch being turned on is changed-over in
SW1a to SWn+1a in a first switch group, under a condition that
a switch SW1b in a second switch group is turned on, in the electric
energy storage apparatus in FIG. 7.

[0056]FIG. 8b is a graph illustrating one example of an output voltage
waveform obtained when a switch being turned on is changed-over in
SW1b to SWn+1b in the second switch group, under a condition
that the switch SW1a in the first switch group is turned on, in the
electric energy storage apparatus in FIG. 7.

[0057]FIG. 9 is a graph illustrating one example of a voltage waveform to
be applied to a load by the electric energy storage apparatus in FIG. 7.

[0058] FIG. 10 is a circuit diagram for explaining a load voltage
deviation occurring when an output voltage changes over time.

[0059] FIG. 11 is a graph illustrating a load voltage deviation occurring
when an output voltage changes over time.

[0060]FIG. 12 is a circuit diagram illustrating an electric energy
storage apparatus with a regenerative function, according to a third
embodiment of the present invention.

[0061]FIG. 13 is a circuit diagram illustrating an electric energy
storage apparatus with a regenerative function, according to a fourth
embodiment of the present invention.

[0062] FIG. 14 is a circuit diagram illustrating a certain electric energy
storage apparatus to explain a voltage outputting method according to a
fifth embodiment of the present invention.

[0063]FIG. 15 is a graph illustrating one example of a half-wave waveform
voltage to be produced by the electric energy storage apparatus in FIG.
14.

[0064]FIG. 16 is a circuit diagram illustrating an electric energy
storage apparatus in which the number of switches is reduced to one-half
as compared to the electric energy storage apparatus in FIG. 14, and a
switch interval is increased two times on the basis of an electric energy
storage element.

[0065]FIG. 17 is a graph illustrating one example of a half-wave waveform
voltage to be produced by the electric energy storage apparatus in FIG.
16.

[0066]FIG. 18 is a graph illustrating one example of a half-wave waveform
voltage to be produced by PWM-controlling the electric energy storage
apparatus in FIG. 16.

[0067]FIG. 19 is a circuit diagram illustrating an electric energy
storage apparatus implementing a method of the present invention and
capable of finely adjusting an output voltage using a small number of
switches.

[0068] FIG. 20 is a circuit diagram illustrating an electric energy
storage apparatus according to a sixth embodiment of the present
invention, wherein a constant-voltage DC power supply is connected to
each electric energy storage module, in place of the balancing circuit.

[0069]FIG. 21 is a circuit diagram illustrating an electric energy
storage apparatus according to the sixth embodiment of the present
invention, wherein a constant-voltage DC power supply is connected to
each electric energy storage module, in place of the balancing circuit.

[0070]FIG. 22 is a circuit diagram illustrating an example of a cell
voltage equalization circuit usable as one example of the balancing
circuit.

[0071]FIG. 23 is a circuit diagram illustrating the circuit in FIG. 22,
wherein each switch in an Sa group is in an ON state, and each
switch in an Sb group is in an OFF state.

[0072]FIG. 24 is a circuit diagram illustrating the circuit in FIG. 22,
wherein each switch in the Sa group is in an OFF state, and each
switch in the Sb group is in an ON state.

DETAILED DESCRIPTION

[0073] In one aspect, particularly in cases where a capacitor having an
output characteristic greatly varying depending on a charged/discharged
state thereof is used as the electric energy storage means, it is
necessary to operate the DC-DC converter in a wide input voltage range so
as to convert the varying output voltage to a voltage falling within a
certain operating range. In this case, the operation of the DC-DC
converter in a wide input voltage range causes a problem of an increase
in loss. Moreover, when the DC-DC converter is a conventional type using
a transformer and a coil, there are other problems, such as a problem
that a circuit size becomes relatively large due to the coil, and a
problem that a weight of the transformer as a whole is increased due to
its components such as an iron core.

[0074] An output voltage of the DC-DC converter is subjected to switching
by the inverter, so as to allow the above electric energy storage
apparatus to generate an AC output. In this process, when a high voltage
is output from the DC-DC converter, switching of the high voltage causes
a problem of an increase in noise.

[0075] Therefore, if an electric energy storage apparatus is provided
which is capable of generating an AC output while minimizing the use of a
DC-DC converter and an inverter, it leads to an improvement in
efficiency, a reduction in noise and a reduction in size of the apparatus
as a whole.

[0076] The electric energy storage apparatus of the present invention is
capable of outputting a DC/AC voltage having a target waveform without
using a module such as a DC-DC converter. In an electric energy storage
apparatus according to a specific embodiment of the present invention, an
inverter also becomes unnecessary.

[0077] This makes it possible to realize an electric energy storage
apparatus capable of outputting a DC/AC voltage in a low-loss and
low-noise manner over a wide output intensity range.

[0079] With reference to the drawings, an electric energy storage
apparatus and a voltage outputting method according to the present
invention will now be described. It is to be understood that a
configuration of an electric energy storage apparatus according to the
present invention is not limited to specific configurations of the
following embodiments illustrated in the figures, but various changes and
modifications may be appropriately made therein without departing from
the spirit and scope thereof as set forth in appended claims. For
example, the following embodiments will be described on the assumption
that each of one or more electric energy storage elements is primarily a
capacitor. Alternatively, the electric energy storage element may be any
chargeable and dischargeable element such as a secondary battery, or a
module composed of a plurality of chargeable and dischargeable elements.
Each of the electric energy storage elements may have a different
capacitance. Further, the following embodiments will be described on the
assumption that each of a plurality of switches is a semiconductor switch
such as MOSFET. Alternatively, any electronic or mechanical switch may be
used.

FIRST EXAMPLE:

Configuration of Electric Energy Storage Apparatus 1

[0080]FIG. 2 is a circuit diagram illustrating an AC output-capable
electric energy storage apparatus 1 according to a first embodiment of
the present invention. The electric energy storage apparatus 1 comprises:
a balancing circuit 2; an electric energy storage module group 3 composed
of n electric energy storage modules (hereinafter referred to as
"capacitors") C1 to Cn connected in series; a switch group 4
composed of n switches SW1 to SWn; and a positive-negative
inversion circuit 5 including switches ISa1, ISa2, ISb1,
ISb2, wherein the electric energy storage apparatus 1 is configured
to apply a voltage to a load 6 in a desired magnitude and polarity. The
load 6 is not limited to a resistor, but may be any load, such as an
element, module or device adapted to be operated by electric power. In
the figure, each of the reference codes A, B indicates a connection point
serving as an input section of the positive-negative inversion circuit 5.

[0081] The balancing circuit 2 may be a circuit comprising an electric
energy storage cell module disclosed, for example, in the Patent Document
1, or may be a circuit configured as a switched capacitor system
comprising capacitors CS1 to CSn-1 and switches Q1 to Q2n,
as illustrated in FIG. 3.

[0082] In cases where the switched capacitor system in FIG. 3 is used as
the balancing circuit 2, the capacitors CS1 to CSn-1, C1
to Cn are subjected to mutual charging and discharging by means of
high-speed changeover of the switches Q1 to Q2n, so that
respective voltages dividedly borne by the capacitors are equalized.

[0083] Specifically, when each of the odd-numbered switches Q1,
Q3, . . . , Q2n-1 is in ON state, capacitors (C1 and
CS1; C2 and CS2, - - - ; CSn-1) are connected in
parallel, respectively. Thus, if a variation in voltage occurs between
the parallel-connected capacitors, mutual charging and discharging are
performed, so that the voltage variation will move toward being
eliminated. On the other hand, when each of the even-numbered switches
Q2, Q4, - - - , Q2n is in an ON state, capacitors (C2
and CS1; C3 and CS2; . . . ; Cn and CSn-1) are
connected in parallel, respectively. Thus, if a variation in voltage
occurs between the parallel-connected capacitors, mutual charging and
discharging are performed, so that the voltage variation will move toward
being eliminated.

[0084] Thus, based on repeatedly performing switching between a mode where
all of the odd-numbered switches are turned on and another mode where all
of the even-numbered switches are turned on, each of the capacitors is
subjected to mutual charging and discharging with respect to all of the
remaining capacitors directly or indirectly (through other capacitors),
so that voltages across the capacitors CS1 to CSn-1, C1 to
Cn are equalized.

[0085] However, it is not essential for the electric energy storage
apparatus 1 of the present invention to equalize voltages across the
capacitors C1 to Cn by the balancing circuit 2.

[0086] Specifically, a magnitude of the output voltage from the electric
energy storage apparatus 1 can be adjusted in increments of a voltage
across each of the capacitors C1 to Cn, as described in detail
later. In this case, it is not essential that voltages across such
electric energy storage elements each serving as a unit for the
adjustment are equal to each other. For example, the balancing circuit 2
may be configured to apply two types of magnitudes of voltages to the
capacitors so as to allow the output voltage to be adjusted in two types
of increments. Alternatively, all of the capacitor voltages may be
adjusted to different values, respectively.

[0087] As each of the electric energy storage modules C1 to Cn
making up the electric energy storage module group 3, it is possible to
use an electric energy storage module composed of two or more capacitors
or secondary batteries (or any other electric energy storage elements),
instead of using a single capacitor. Even in cases where two or more
capacitors or secondary batteries are connected in series or in parallel,
it can be handled as with a capacitor by appropriately calculating a
composite capacitance thereof.

[0088] Each of the switches SW1 to SWn comprised in the switch
group 4 is disposed in a path connecting a terminal of one of the
capacitors C1 to Cn and the connection point A within the
electric energy storage apparatus 1. When one of the switches SW1 to
SWn is turned on, a terminal of the selected switch is electrically
connected to the connection point A, so that, depending on the selected
switch, a voltage obtained by summing voltages across one or more of the
capacitors C1 to Cn is applied between the connection point A
and the connection point B.

[0089] The positive-negative inversion circuit 5 is configured to perform
changeover among the switches ISa1, ISa2, ISb1, ISb2
to select an output terminal of the electric energy storage apparatus 1
to be connected to the connection points A, B. Specifically, a polarity
of a voltage to be applied to the load 6 can be selected depending on
whether the switches ISa1, ISa2 are turned on, or switches
ISb1, ISb2 are turned on. It is to be noted that the above
configuration using four switches is simply described as one example of
the positive-negative inversion circuit 5, and any other suitable circuit
capable of selecting a polarity of the output voltage may be used to
implement the electric energy storage apparatus 1 of the present
invention.

[0091] The reference waveform oscillating circuit 7 is configured to
output a reference waveform signal representing a target output voltage
waveform which is a voltage to be output from the electric energy storage
apparatus 1. Typically, the electric energy storage apparatus 1 operates
to output a voltage obtained by multiplying an instantaneous voltage in
the reference waveform signal output from the reference waveform
oscillating circuit 7, by a certain magnification value.

[0092] The voltage detection circuit 8 is configured to detect a voltage
across at least one of the capacitors C1 to Cn, or voltages
across all of the respective capacitors C1 to Cn. Typically,
the voltage detection circuit 8 is configured such that it is connected
to the capacitors C1 to Cn to directly detect voltages across
the respective capacitors C1 to Cn and output the detected
voltages to the comparison and calculation circuit 9. Alternatively, for
example, the voltage detection circuit 8 may be configured such that it
is connected to an arbitrary element in the balancing circuit to detect a
voltage across the element, and then a voltage across each of the
capacitors is calculated based on a value of the detected voltage.

[0093] The voltage detection circuit 8 may be configured to directly
detect a voltage across the load 6, instead of the capacitor voltage, as
previously described. This is because a specific mathematical
relationship is established between the electric energy storage module
voltage and the load voltage, depending on one of the switches to be
selectively turned on, and thereby it is only necessary to detect one of
them so as to adjust an output voltage. Although not illustrated, in such
a case, the voltage detection circuit 8 is connected to the load 6,
instead of the electric energy storage module group 3.

[0094] The comparison and calculation circuit 9 is configured to compare a
target voltage determined based on a voltage of the reference waveform
signal output from the reference waveform oscillating circuit 7
(typically, the target voltage is determined as a voltage having a
polarity and a magnitude obtained by multiplying the voltage of the
reference waveform signal by a certain magnification value), with a
capacitor voltage output from the voltage detection circuit 8, and output
a signal to the switch control circuit 10.

[0095] For example, the signal may be a signal simply indicative of a
ratio between the target voltage and the capacitor voltage.
Alternatively, the specific signal may be a signal for informing of a
deviation between the target voltage and an output voltage, wherein the
comparison and calculation circuit 9 is operable to: receive information
about a present switch changeover state from the switch control circuit
10, while receiving a value of the capacitor voltage from the voltage
detection circuit 8; calculate a magnitude of a voltage presently output
from the electric energy storage apparatus 1, based on the received
switch changeover state and the received capacitor voltage value; and
calculate the deviation between the target voltage and the output
voltage. Alternatively, the comparison and calculation circuit 9 may be
configured to determine a switch changeover state to be selected, based
on the above information, and output a changeover instruction signal to
the switch control circuit 10.

[0096] The switch control circuit 10 is configured to, based on a signal
received from the comparison and calculation circuit 9, output a switch
changeover signal to the switch group 4.

[0097] In cases where a semiconductor switch, such as MOSFET, is used as
each of the switches SW1 to SWn, the switch changeover signal
may be an RF signal to be generated, for example, by an RF oscillation
circuit in the switch control circuit 10. In cases where a mechanical
switch is used as each of the switches SW1 to SWn, for example,
the switch control circuit 10 may be appropriately configured to generate
a suitable control signal depending on a specific operating principle of
the switch.

[0098] The positive-negative inversion control circuit 11 is configured to
send a control signal to the positive-negative inversion circuit 5 so as
to change a polarity of an output voltage according to need. In cases
where the switch-based configuration illustrated in

[0099]FIG. 2 is used as the positive-negative inversion circuit 5, the
positive-negative inversion control circuit 11 may be any switch driver
as with the switch control circuit. However, the positive-negative
inversion control circuit 11 is not limited thereto, but any other
suitable circuit capable of controlling the operation of the
positive-negative inversion circuit 5 may be used depending on a specific
configuration of the positive-negative inversion circuit 5. The signal
for informing of a polarity of a voltage to be output may be input from
the comparison and calculation circuit 9 into the positive-negative
inversion control circuit 11 via the switch control circuit 10, or may be
input from the comparison and calculation circuit 9 directly into the
positive-negative inversion control circuit 11.

[0100] In the operation of the electric energy storage apparatus according
to the present invention, the group of circuits 7 to 11 can be
advantageously used to automatically perform control during the
operation. However, the circuit group is not essential, but the electric
energy storage apparatus 1 according to the present invention may be
operated under connection with any suitable external device or under
control of any suitable external system.

[0101] In FIG. 2, the reference waveform oscillating circuit 7, the
voltage detection circuit 8, the comparison and calculation circuit 9,
the switch control circuit 10 and the positive-negative inversion control
circuit 11 are illustrated as independent circuits, respectively.
Alternatively, the circuits may be replaced with a single circuit
incorporating all functions thereof. Alternatively, a function of each of
the circuits may be borne by two or more arbitrary number of circuits.

Operation of Electric Energy Storage Apparatus 1

[0102] The operation of the electric energy storage apparatus 1 will be
described below. In an initial state, the capacitors C1to Cn
are charged at predetermined voltages, respectively. The voltages may be
different from each other, as discussed above. As one example, the
following description will be made on the assumption that the same
voltage is applied to all of the capacitors. Further, assuming that each
of the switches SW1 to SWn is in an OFF state, and an arbitrary
changeover state is selected in the positive-negative inversion circuit
5.

[0103] The comparison and calculation circuit 9 is in a standby state
capable of receiving an input of respective signals from the reference
waveform oscillating circuit 7 and the voltage detection circuit 8. As
one example, the comparison and calculation circuit 9 is operable to
ascertain respective signals from the reference waveform oscillating
circuit 7 and the voltage detection circuit 8 at intervals of a
predetermined period of time determined, for example, by a clock
frequency of a processing unit (not illustrated) constituting the
comparison and calculation circuit 9, and, when both of the signals are
present, to execute comparison and calculation.

[0104] Upon input of signals from the reference waveform oscillating
circuit 7 and the voltage detection circuit 8 into the comparison and
calculation circuit 9, the comparison and calculation circuit 9 compares
an instantaneous voltage value of the reference waveform signal input
from the reference waveform oscillating circuit 7, with a capacitor
voltage input from the voltage detection circuit 8.

[0105] For example, assuming that the instantaneous voltage value of the
reference waveform signal is +50 mV, and the voltage across each of the
capacitors C1 to Cn is 1V. As a preset magnification value of
the electric energy storage apparatus 1, a preliminary setting may be
made in which an output is 100 times the reference waveform (typically,
based on a setting signal to be input into the comparison and calculation
circuit 9 from the reference waveform oscillating circuit 7 or through
any suitable external interface). In this case, the comparison and
calculation circuit 9 compares the capacitor voltage 1V, with 5V which is
100 times the instantaneous voltage value of the reference waveform
signal, and outputs, to the switch control circuit 10, a signal
indicative of "5" which is a ratio therebetween and a signal indicative
of "+" which is a polarity of the voltage of the reference waveform
signal (or directly outputs a signal indicative of "+5V" which is a
target output voltage).

[0106] The switch control circuit 10 selects a changeover state of the
switch group 4 to be selected, according to the signals input thereinto.
When a signal indicative of "5" as a ratio is input, it is necessary to
select a voltage corresponding to five capacitors, as a magnitude of a
target output voltage. Thus, the switch control circuit 10 outputs, to
the switch group 4, a switch changeover signal for turning on the switch
SW5. (Alternatively, the switch control circuit 10 may be configured
to, based on a signal indicative of "+5V" as a target output voltage
received from the comparison and calculation circuit 9, and a capacitor
voltage received from the voltage detection circuit 8, make a
determination that the switch SW5 should be turned on, and then
output a switch changeover signal for turning on the switch SW5.)

[0107] When the switch SW5 is turned on by the switch changeover
signal, a 5V voltage which is a sum of voltages across the respective
capacitors C1 to C5 is applied between the connection points A,
B.

[0108] After being output from the comparison and calculation circuit 9,
the signal indicative of "+" which is a polarity of the instantaneous
voltage value of the reference waveform signal, i.e., a polarity of the
target output voltage, is input into the positive-negative inversion
control circuit 11 through the switch control circuit 10 (or directly).
The positive-negative inversion control circuit 11 is preliminarily set
such that the switch ISa1 and the switch ISa2 correspond to the
"+" signal, and the switch ISb1 and the switch ISb2 correspond
to a "-" signal (or to a converse correspondence relationship). Thus,
when the positive-negative inversion control circuit 11 receives the "+"
signal, it outputs, to the positive-negative inversion circuit 5, a
control signal for turning on the switches ISa1, ISa2.

[0109] When the switches ISa1, ISa2 in the positive-negative
inversion circuit 5 are turned on by the control signal, the "+5V"
voltage, i.e., target output voltage, is applied to the load 6.

[0110] The operation of adjusting the output voltage according to an
instantaneous voltage value of the reference waveform signal at a certain
clock time is performed in the above manner. According to the above
adjustment operation, the output voltage is adjusted at intervals of a
predetermined period of time, based primarily on a clock frequency
determined by the comparison and calculation circuit 9, depending on
momentarily varying instantaneous values of the target output voltage.
The electric energy storage apparatus 1 is capable of selectively
outputting a DC voltage and an AC voltage depending on reference waveform
signals.

[0111] Not only based on the instantaneous value of the target output
voltage but also when the capacitor voltage is lowered due to discharge
of the capacitors C1 to C5, the switch changeover is adequately
performed according to the above operation.

[0112] For example, assuming that a signal input from the reference
waveform oscillating circuit 7 into the comparison and calculation
circuit 9 indicates "+50 mV", i.e., the same instantaneous voltage value
of the reference waveform signal as before. On the other hand, assuming
that a signal input from the voltage detection circuit 8 indicates a
voltage across each of the capacitors C1 to Cn is 0.5V (which
corresponds to a phenomenon that a voltage drop occurs in each of the
capacitors C1 to Cn due to discharge caused by continuous
voltage application to the load 6. Even if only the capacitors C1 to
C5 are directly connected to the load 6, a voltage drop equally
occurs in the capacitors C1 to Cn by the operation of the
balancing circuit 2).

[0113] The comparison and calculation circuit 9 compares the capacitor
voltage 0.5V, with 5V which is 100 times the instantaneous voltage value
of the reference waveform signal, and outputs, to the switch control
circuit 10, a signal indicative of "10" which is a ratio therebetween and
a signal indicative of "+" which is a polarity of the target voltage.

[0114] The switch control circuit 10 selects a changeover state of the
switch group 4, according to the signals input thereinto. When a signal
indicative of "10" as a ratio is input, it is necessary to select a
voltage corresponding to ten capacitors, as a magnitude of a target
output voltage. Thus, the switch control circuit 10 outputs, to the
switch group 4, a switch changeover signal for turning on the switch
SW10 (not illustrated).

[0115] When the switch SW10 is turned on by the switch changeover
signal, a 5V voltage which is a sum of voltages across the respective
capacitors C1 to C10 (not illustrated) is applied between the
connection points A, B.

[0116] After being output from the comparison and calculation circuit 9,
the signal indicative of "+" which is a polarity of the target output
voltage, is input into the positive-negative inversion control circuit 11
through the switch control circuit 10 (or directly). Thus, when the
positive-negative inversion control circuit 11 receives the "+" signal,
it outputs, to the positive-negative inversion circuit 5, a control
signal for turning on the switches ISa1, ISa2.

[0117] When the switches ISa1, ISa2 in the positive-negative
inversion circuit 5 are turned on by the control signal (if such a state
has already been selected, the switch changeover is unnecessary), the
"+5V" voltage is applied to the load 6.

[0118] As above, based on continuously monitoring a capacitor voltage by
the voltage detection circuit 8, it becomes possible to prevent a
disturbance of the output voltage due to a voltage drop in the
capacitors.

[0119]FIG. 4 is a graph illustrating one cycle of a voltage which is
output between the connection points A, B when a sine wave is input as
the target output voltage. During one cycle, an actual sine wave is
changed between a positive polarity and a negative polarity. However, the
polarity change is not reflected on changeover among the switch group 4,
and a voltage having the same polarity is output between the connection
points A, B. This voltage is input into the positive-negative inversion
circuit, and subjected to conversion corresponding to the polarity of the
target output voltage at each clock time.

[0120] In the graph illustrated in FIG. 4, the output voltage to the
connection points A, B changes in a stepwise manner at constant time
intervals, instead of changing in a continuous manner. This is because
the electric energy storage apparatus 1 is configured to adjust the
output voltage at intervals of a predetermined period of time, as
previously discussed.

[0121] In the example illustrated in FIG. 4, the adjustment of the output
voltage is performed 16 times during one cycle of the reference waveform
signal. It is to be understood that the predetermined period of time may
be shortened to obtain a smoother output voltage waveform.

[0122]FIG. 5 is a diagram illustrating a switch changeover to be
performed to compensate for an influence of voltage drop in the
capacitors. When a voltage is continuously applied to the load 6, each of
the capacitors C1 to Cn is discharged, and a voltage across
each of the capacitors C1 to Cn is lowered, as previously
discussed. Therefore, even if a sine wave having a constant amplitude
characteristic is input as the reference waveform signal, the number of
capacitors required for outputting a voltage having a magnitude
corresponding to the constant amplitude characteristic will be increased
over time.

[0123] The graph drawn by the solid line in FIG. 5 indicates a temporal
change in a selected one of the switches to output a sine wave
corresponding to the reference waveform signal over a certain half cycle.
On the other hand, the broken line in FIG. 5 indicates a temporal change
in a selected one of the switches to output a sine wave corresponding to
the reference waveform signal over another half cycle temporally
subsequent to the certain half cycle. FIG. 5 shows that the number of
capacitors contributing to an output has to be increased over time to
output a voltage value in a sine wave having the same amplitude
characteristic and in the same phase characteristic (assuming here that a
cycle of the sine wave is sufficiently shorter than a discharge time of
the capacitor. If such conditions cannot be established, the graph in
FIG. 5 is corrected to a curve extending rightwardly and upwardly over
time even in the same half cycle.)

[0124] In cases where certain charging means is incorporated in the
balancing circuit 2, or a constant-voltage DC power supply is connected
to the capacitors C1 to Cn, as described in an aftermentioned
sixed embodiment, the voltage across each of the capacitors C1 to
C5 is kept constant, so that the switch changeover for coping with
the voltage drop is unnecessary.

[0125]FIG. 6 is a graph illustrating an output voltage from the electric
energy storage apparatus 1 when a sine wave is input as the reference
waveform signal. This voltage is applied to the load 6 as an output of
the electric energy storage apparatus 1. Such the waveform corresponds to
an AC voltage realized when the voltage illustrated in FIG. 4 is
subjected to adequate polarity conversion in the positive-negative
inversion circuit 5.

SECOND EXAMPLE

Configuration of Electric Energy Storage Apparatus 1

[0126]FIG. 7 is a circuit diagram illustrating an AC output-capable
electric energy storage apparatus 1 according to a second embodiment of
the present invention. Differently from the electric energy storage
apparatus in FIG. 1, the electric energy storage apparatus 1 according to
the second embodiment is devoid of the positive-negative inversion
circuit 5 and the positive-negative inversion control circuit 11, and the
switch group 4 comprises a first switch group 12 composed of switches
SW1a to SWn+1a, and a second switch group 13 composed of
switches SW1b to SWn+1b.

[0127] Each of the switches SW1a to SWn+1a in the first switch
group 12 is disposed in a path connecting a terminal of one of n
capacitors C1 to Cn and a connection point A within the
electric energy storage apparatus 1. Each of the switches SW1b to
SWn+1b in the second switch group 13 is disposed in a path
connecting a terminal of one of the capacitors C1 to Cn and a
connection point B within the electric energy storage apparatus 1. The
electric energy storage apparatus 1 in FIG. 7 is devoid of the
positive-negative inversion circuit 5, so that a load 6 is connected
between the connection points A, B. Thus, the connection points A, B will
hereinafter referred to as "output terminals A, B".

[0128] The configuration illustrated in FIG. 7 is capable of changing a
polarity of an output voltage without using the positive-negative
inversion circuit. As one example, when each of the switch SW5a in
the first switch group 12 and the switch SW2b in the second switch
group 13 is in an ON state, an output voltage corresponding to a sum of
voltages across the respective capacitors C2, C3, C4 is
applied to the load 6. In this state, a polarity of the output voltage
can be changed by performing a switch changeover in each of the switch
groups in such a manner that the switch SW2a in the first switch
group 12 and the switch SW5b in the second switch group 13 are
turned on.

[0129] The remaining components are the same as those in the electric
energy storage apparatus illustrated in FIG. 2. Each component, circuit,
element or module is not limited to the illustrated specific
configuration, but various changes and modifications may be appropriately
made therein without departing from the spirit and scope thereof as set
forth in appended claims.

Operation of Electric Energy Storage Apparatus 1

[0130] An operation of the electric energy storage apparatus 1 configured
as illustrated in FIG. 7 will be described below. In an initial state,
the capacitors C1 to Cn are charged at predetermined voltages,
respectively. The voltages may be different from each other, as discussed
above. As one example, the following description will be made on the
assumption that the same voltage is applied to all of the capacitors.
Further, assuming that all switches in at least one of the group of
switches SW1a to SWn+1a and the group of switches SW1b to
SWn+1b are in an OFF state, so that no voltage is applied from the
electric energy storage apparatus 1 to the load 6.

[0131] A comparison and calculation circuit 9 is in a standby state
capable of receiving an input of respective signals from a reference
waveform oscillating circuit 7 and a voltage detection circuit 8. As one
example, the comparison and calculation circuit 9 is operable to
ascertain respective signals from the reference waveform oscillating
circuit 7 and the voltage detection circuit 8 at intervals of a
predetermined period of time determined, for example, by a clock
frequency of a processing unit (not illustrated) constituting the
comparison and calculation circuit 9, and, when both of the signals are
present, to execute comparison and calculation.

[0132] Upon input of signals from the reference waveform oscillating
circuit 7 and the voltage detection circuit 8 into the comparison and
calculation circuit 9, the comparison and calculation circuit 9 compares
an instantaneous voltage value of a reference waveform signal input from
the reference waveform oscillating circuit 7, with a capacitor voltage
input from the voltage detection circuit 8.

[0133] For example, assuming that the instantaneous voltage value of the
reference waveform signal is +50 mV, and the voltage across each of the
capacitors C1 to Cn is 1V. As a preset magnification value of
the electric energy storage apparatus 1, a preliminary setting may be
made in which an output is 100 times the reference waveform (typically,
based on a setting signal to be input into the comparison and calculation
circuit 9 through any suitable interface). In this case, the comparison
and calculation circuit 9 compares the capacitor voltage 1V, with 5V
which is 100 times the instantaneous voltage value of the reference
waveform signal, and outputs, to the switch control circuit 10, a signal
indicative of "5" which is a ratio therebetween and a signal indicative
of "+" which is a polarity of the voltage of the reference waveform
signal.

[0134] The switch control circuit 10 selects a changeover state of each of
the first switch group 12 and the second switch group 13, according to
the signals input thereinto. When a signal indicative of "5" as a ratio
is input, it is necessary to select a voltage corresponding to five
capacitors, as a magnitude of a target output voltage. Thus, for example,
the switch control circuit 10 outputs a signal for turning on the switch
SW6a, and a signal for turning on the switch SW1b, to the first
switch group 12 and the second switch group 13, respectively, or outputs
a signal for turning on the switch SW1a, and a signal for turning on
the switch SW6b, to the first switch group 12 and the second switch
group 13, respectively.

[0135] The selection of the changeover states is determined by a polarity
of the instantaneous voltage of the reference waveform signal indicated
by the signal from the comparison and calculation circuit 9, i.e., a
polarity of the target output voltage. As one example, a preliminary
setting may be made such that, when the polarity is "+", one of the
switches to be selected from the first switch group 12 has a suffix
number which is equal to or greater than that of one of the switches to
be selected from the second switch group 13 (typically, based on an input
into the switch control circuit 10 through any suitable interface). In
this case, a switch changeover signal for turning on the switch SW6a
and a switch changeover signal for turning on the switch SW1b are
output to the first switch group 12 and the second switch group 13,
respectively.

[0136] Alternatively, a preliminary setting may be made such that, when
the polarity is "+", the switch SW1b in the second switch group is
turned on, and, when the polarity is "-", the switch SW1a in the
first switch group is turned on. In other words, a voltage reference
point is fixedly set depending on a polarity. Then, when the polarity is
"+", a suitable one of the switches is selected from the first switch
group, and, when the polarity is "-", a suitable one of the switches is
selected from the second switch group, so that it becomes possible to
adjust an output voltage according to a magnitude of the target output
voltage. This configuration is capable of coping with a change in the
target output voltage by performing a switch changeover in only one of
the first and second switch groups at any timing, except a timing of
change in polarity of the target output voltage, which makes it possible
to further reduce noise due to switch changeover.

[0137] As above, based on the adequate changeover between the first switch
group 12 and the second switch group 13, a "+5V" voltage which is the
target output voltage is applied to the load 6.

[0138] The operation of adjusting the output voltage according to an
instantaneous voltage value of the reference waveform signal at a certain
clock time is performed in the above manner. According to the above
adjustment operation, the output voltage is adjusted at intervals of a
predetermined period of time, based primarily on a clock frequency
determined by the comparison and calculation circuit 9, depending on
momentarily varying instantaneous values of the target output voltage.
The electric energy storage apparatus 1 is capable of selectively
outputting a DC voltage and an AC voltage depending on reference waveform
signals.

[0139] Not only based on the instantaneous value of the target output
voltage but also when the capacitor voltage is lowered due to discharge
of the capacitors C1 to C5, the switch changeover is adequately
performed according to the above operation, as with the electric energy
storage apparatus illustrated in FIG. 2.

[0140] Based on continuously monitoring a capacitor voltage by the voltage
detection circuit 8, it becomes possible to prevent a disturbance of the
output voltage due to a voltage drop in each capacitor, as previously
discussed.

[0141] FIGS. 8a and 8b are graphs each illustrating a half cycle of a
voltage which is output between the output terminals A, B when a sine
wave is input as the reference waveform signal, wherein FIG. 8a
illustrates an initial half cycle, and FIG. 8b illustrates a subsequent
half cycle. Specifically, FIG. 8a illustrates a voltage which is output
in the initial half cycle by turning on one of the switches in the first
switch group 12 in a selectively changing-over manner in conformity to a
sine-waveform, under a condition that the switch SW1b in the second
switch group 13 is turned on, and FIG. 8b illustrates a voltage which is
output in the subsequent half cycle by turning on one of the switches in
the second switch group 13 in a selectively changing-over manner in
conformity to the sine-waveform, under a condition that the switch
SW1a in the first switch group 12 is turned on. Based on the
adequate changeover between the first switch group 12 and the second
switch group 13, it becomes possible to cope with the polarity change, so
that a voltage having an arbitrary waveform involving a polarity change
can be output without using the positive-negative inversion circuit. FIG.
9 illustrates an AC voltage involving a polarity change, which is output
over one cycle by the electric energy storage apparatus 1 illustrated in
FIG. 7.

[0142] As with the first embodiment, the output voltage from the output
terminals A, B changes in a stepwise manner at constant time intervals,
instead of changing in a continuous manner. This is because the electric
energy storage apparatus 1 is configured to adjust the output voltage at
intervals of a predetermined period of time, as previously discussed. It
is to be understood that the predetermined period of time may be
shortened to obtain a smoother output voltage waveform.

[0143] In addition, also in the electric energy storage apparatus 1
illustrated in FIG. 7, when a voltage is continuously applied to the load
6, each of the capacitors C1 to Cn is discharged, and a voltage
across each of the capacitors C1 to Cn is lowered. Therefore,
even if a sine wave having a constant amplitude characteristic is input
as the reference waveform signal, the number of capacitors required for
outputting a voltage having a magnitude corresponding to the constant
amplitude characteristic will be increased over time. Thus, it is
preferable to perform the switch changeover as illustrated in FIG. 5 in
the same manner as that in the first embodiment.

[0144] In cases where certain charging means is incorporated in the
balancing circuit 2, or a constant-voltage DC power supply is connected
to the capacitors C1 to Cn, as described in the aftermentioned
sixed embodiment, the voltage across each of the capacitors C1 to
C5 is kept constant, so that the switch changeover for coping with
the voltage drop is unnecessary.

THIRD EXAMPLE

Configuration of Electric Energy Storage Apparatus 1

[0145]FIG. 12 is a circuit diagram illustrating an electric energy
storage apparatus 1 with a regenerative function, according to a third
embodiment of the present invention. As compared to the electric energy
storage apparatus in FIG. 2, the electric energy storage apparatus 1
according to the third embodiment additionally comprises a load voltage
detection circuit 14, a comparison and feedback circuit 15 and a
regeneration switch control circuit 16.

[0146] The electric energy storage apparatus 1 in FIG. 12 is capable of,
even if a load voltage deviates from a target voltage value obtained by
multiplying a voltage of a reference waveform signal by a preset
magnification value, correcting the deviation, and regeneratively
returning, to capacitors, excess energy of a load 6 corresponding to the
deviated voltage, to compensate for voltage drop in the capacitors to
some extent.

Operation of Electric Energy Storage Apparatus 1

[0147] Before explaining a regenerative function realizable by the
electric energy storage apparatus 1 illustrated in FIG. 12, a load
voltage deviation as a factor requiring the regenerative function will be
described below.

[0148] FIG. 10 illustrates one example of an electric energy storage
apparatus convenient for explaining a load voltage deviation. The
electric energy storage apparatus 17 comprises a balancing circuit 18, a
capacitor group 19 composed of eight capacitors C1 to C8, and a
switch group 20 composed of eight switches SW1 to SW8, wherein
it is configured to turn on one of the switches in a selectively
changing-over manner to output a time-dependent voltage to a load 21.

[0149] FIG. 11 is a graph illustrating a load voltage deviation from a
desired value, occurring when the electric energy storage apparatus 17
outputs a voltage changing over time.

[0150] In the electric energy storage apparatus 17, when the switches
SW1 to SW8 are sequentially turned on in order of SW1,
SW2, . . . , SW8, at intervals of a predetermined period of
time, a current flows from each of the capacitors through the load 21, so
that a load voltage is raised in a stepwise manner. A width of each step
corresponds to a voltage across each of the capacitors C1 to
C8.

[0151] Considering a situation where, after turning on the SW8 to
apply a maximum voltage to the load 21, the switches SW1 to SW8
are sequentially turned on in order of SW7, SW6, . . . ,
SW1, to lower the load voltage in a pattern symmetrical to that
during the rising.

[0152] In this case, if the load 21 is a desired sufficiently heavy
resistor, the load voltage is lowered in a stepwise pattern symmetrical
to that during the rising, as indicated by a broken line in FIG. 11.
However, if the load 21 comprises a reactive element, such as a coil and
a capacitor, or if the load 21 is light, or if the load 21 has a certain
reactance component due to its shape, wherein the reactance component is
unignorably large as compared to a resistance component, a lowering
pattern of the load voltage will deviate from the desired pattern, as
indicated by the solid line. As one example, such a deviation occurs when
an induced electromotive force is generated within the load 21.

[0153] The electric energy storage apparatus 1 in FIG. 12 is capable of
correcting such a load voltage deviation from a desired pattern. With a
focus on this point, an operation of the electric energy storage
apparatus 1 will be described below.

[0154] Except for an operation concerning the correction of a load voltage
deviation, the electric energy storage apparatus 1 in FIG. 12 operates in
the same manner as that in the electric energy storage apparatus
illustrated in FIG. 2. Specifically, in a comparison and calculation
circuit 9, an instantaneous voltage value of a reference waveform signal
input from a reference waveform oscillating circuit 7 is compared with a
capacitor voltage input from a voltage detection circuit 8. Then, the
number of capacitors required for contributing to a voltage output to the
load is determined depending on a preset magnification value, and a
corresponding switch changeover signal is output to a switch group 4 to
select a magnitude of an output voltage. Further, a control signal
corresponding to a (positive/negative) polarity of the instantaneous
voltage value of the reference waveform signal input from the reference
waveform oscillating circuit 7 is output to a positive-negative inversion
circuit 5 to select a polarity of the output voltage to be applied to the
load.

[0155] As a new operation to be performed by the electric energy storage
apparatus 1 in FIG. 12, the load voltage detection circuit 14 is operable
to monitor a voltage across the load 6, and output a signal indicative of
a detected voltage to the comparison and feedback circuit 15.
Additionally, a signal indicative of a target output voltage is input
from the reference waveform oscillating circuit 7 into the comparison and
feedback circuit 15. The respective output/input timings of the two
signals may be synchronized by a certain external device, or, each of the
load voltage detection circuit 14 and the reference waveform oscillating
circuit 7 may be configured to output the signal to the comparison and
feedback circuit 15 at intervals of a predetermined period of time
determined, for example, by a clock frequency set for each of them.
Alternatively, signals indicative of the instantaneous voltage value of
the reference waveform signal and the preset magnification value may be
input from the reference waveform oscillating circuit 7 or any other
module constituting the electric energy storage apparatus 1, into the
comparison and feedback circuit 15. Alternatively, the electric energy
storage apparatus 1 may be configured such that the preset magnification
value is preliminarily input into the comparison and feedback circuit 15
directly through an arbitrary external interface.

[0156] The comparison and feedback circuit 15 is operable, based on a load
voltage informed by the signal from the load voltage detection circuit
14, and a target output voltage informed by the signal from the reference
waveform oscillating circuit 7, to calculate a load voltage deviation
from the target output voltage. Subsequently, as one example, the
comparison and feedback circuit 15 is operable to generate a signal
indicative of a difference between the load voltage and the target
voltage, and output the signal to the regeneration switch control circuit
16. Alternatively, the comparison and feedback circuit 15 may be
configured to, only when the difference between the load voltage and the
target voltage is greater than an allowable limit value, output the
signal to the regeneration switch control circuit 16.

[0157] The regeneration switch control circuit 16 is operable, in response
to the signal from the comparison and feedback circuit 15, to output a
switch changeover signal to the switch group 4 (when the signal
indicative of the difference between the load voltage and the target
voltage is input from the comparison and feedback circuit 15, the switch
changeover signal is output on condition that a value of the difference
is greater than an allowable limit value). When the switch group 4
receives the switch changeover signal, one of the switches set to an ON
state to apply the output voltage to the load is opened once, and then
one of the switches in the switch group 4 is newly selected and turned
on.

[0158] In the above operation, the switch SW1 is typically turned on.
Consequently, only the capacitor C1 is connected to the load 6, and
excess energy is regeneratively returned from the load 6 to the capacitor
C1 due to a potential difference therebetween. It is not essential
to select the switch SW1 so as to perform the regeneration. However,
in view of increasing the potential difference from the load 6 to obtain
a higher regenerative speed, it is preferable to select the switch
SW1 to minimize the number of ones of the capacitors which are to be
connected to the load 6.

[0159] In this example, the regeneration of excess energy means discharge
from the load 6 to the capacitor C1, so that the voltage across the
load 6 is lowered to become closer to the target value, and the voltage
across the capacitor C1 is increased.

[0160] Voltages across the respective capacitors C1 to Cn are
continually adjusted by a balancing circuit 2. Thus, in the electric
energy storage apparatus employing the balancing circuit 2 for voltage
equalization, the energy charged in the capacitor C1 is distributed
over the remaining capacitors C2 to Cn by the balancing circuit
2 to increase those respective capacitor voltages. This makes it possible
to extend an operable time of the electric energy storage apparatus 1.

[0161] After an elapse of a predetermined time from the turn-on of the
switch SW1, the switch SW1 is turn off, and a switch changeover
signal is output from the switch control circuit 10 to the switch group 4
so as to return the switch group 4 to a changeover state just before
start of the regeneration. The information on the elapse of the
predetermined time may be given from a certain external device for
controlling an operation timing of the entire electric energy storage
apparatus. Alternatively, the electric energy storage apparatus may be
configured to output a signal indicative of the elapse of the
predetermined time, from the regeneration switch control circuit 16 to
the switch control circuit 10.

[0162] Instead of using the elapse of the predetermined time as a
condition for a switch changeover, the electric energy storage apparatus
1 may be configured such that the load voltage is compared with the
target value by the comparison and feedback circuit 15 as needed, while
detecting the load voltage by the load voltage detection circuit 14 even
during the regeneration operation, and, when a difference between the
load voltage and the target value becomes less than an allowable limit
value, a control signal is output from the comparison and feedback
circuit 15 to the switch control circuit 10 to return the switch group 4
to a changeover state just before start of the regeneration operation.

[0163] The subsequent operation is the same as that in the electric energy
storage apparatus illustrated in FIG. 2. A magnitude and polarity of the
output voltage is adjusted based on momentarily changing inputs from the
reference waveform oscillating circuit 7 and the voltage detection
circuit 8.

[0164] In the third embodiment, a timing of performing the regeneration
operation may be arbitrarily set. For example, the electric energy
storage apparatus 1 may be configured to perform the regeneration
operation at intervals of the same period of time as the predetermined
period of time for the adjustment of the output voltage, i.e., in
conjunction with each adjustment of the output voltage, based on the
inputs from the reference waveform oscillating circuit 7 and the voltage
detection circuit 8. Further, the electric energy storage apparatus 1 may
be configured to perform the comparison in the comparison and feedback
circuit 15 at intervals of a period of time different from the above
predetermined period of time.

FOURTH EXAMPLE

[0165] The configuration for the regeneration operation may be
incorporated in the electric energy storage apparatus illustrated in FIG.
7. FIG. 13 illustrates a configuration of this electric energy storage
apparatus.

[0166] As with the electric energy storage apparatus in FIG. 12, a load
voltage detection circuit 14 is operable to monitor a voltage of a load
6, and a comparison and feedback circuit 15 is operable to compare the
load voltage with a target value, and, according to a comparison result,
to temporarily change a switch group 4 to a switch changeover state for
performing a regenerating operation.

[0167] In the electric energy storage apparatus illustrated in FIG. 13,
the switch group 4 comprises a first switch group 12 and a second switch
group 13. Thus, in the regeneration operation, a switch to be turned on
is selected from each of the first switch group 12 and the second switch
group 13.

[0168] In view of a higher regenerative speed, it is preferable to select
the switches to apply, to the load 6, a voltage having a reverse polarity
with respect to that of the load voltage and a large magnitude. However,
this involves a risk of damage to the capacitor due to a large current
flowing therein, and a problem that energy of the load 6 is lost beyond a
correction range. Thus, the switch changeover state to be employed in the
regeneration operation should be set depending on various conditions,
such as characteristics of each element and a level of temporal change in
the target output voltage, on a case-by-case basis. It will be apparent
to those skilled in the art to appropriately perform such a setting
according to teaching of the present invention. Therefore, unless
otherwise such variations depart from the scope of the present invention
hereinafter defined, they should be construed as being included therein.

FIFTH EXAMPLE

[0169] A voltage outputting method according to a fifth embodiment of the
present invention will be described below. This method may be implemented
by using any one of the electric energy storage apparatuses in FIGS. 2,
7, 12 and 13, and designed to finely adjust a substantial output voltage
as a meaning of a temporal average value, using a small number of
elements.

[0170] FIGS. 14 and 16 illustrate examples of an electric energy storage
apparatus 22 convenient for explaining a problem with an increment width
in output voltage adjustment. In each example, the electric energy
storage apparatus 22 comprises a balancing circuit 23, a capacitor group
24 composed of the same number of capacitors C1 to C8, and a
switch group 25 (26), wherein it is configured to turn on one of the
switches in a selectively changing-over manner to output a time-dependent
voltage to a load 27. The switch group 25 is different from the switch
group 26 in that the switch group 25 is composed of eight switches
SW1 to SW8, whereas the switch group 26 is composed of four
switches SW1 to SW4.

[0171] In the electric energy storage apparatus 22 illustrated in FIG. 14,
the number of capacitors contributing to the output voltage can be
selected in increments of one capacitor by turning on one of the switches
SW1 to SW8. On the other hand, in the electric energy storage
apparatus illustrated in FIG. 15, the number of capacitors contributing
to the output voltage can be selected only in increments of two
capacitors by turning on one of the switches SW1 to SW4.

[0172]FIG. 15 illustrates an output voltage obtained when the switches in
the electric energy storage apparatus in FIG. 14 are sequentially turned
on under a condition that the balancing circuit 23 is configured to
equalize the capacitor voltages. Assuming that a voltage across each of
the capacitors is V, the output voltage is adjusted to (0), V, 2V, . . .
, 8V by sequentially turning on the switches in order of (each switch is
in an OFF state), SW1, SW2, . . . , SW8, or adjusted to
8V, 7V, . . . V, (0) by sequentially turning on the switches in order of
SW8, SW7, . . . SW1, (each switch is in the OFF state). In
other words, the output voltage is adjusted in increments of V.

[0173]FIG. 17 illustrates an output voltage obtained when the switches in
the electric energy storage apparatus in FIG. 16 are sequentially turned
on under a condition that the balancing circuit 23 has the same
configuration as above. Assuming that a voltage across each of the
capacitors is V, the output voltage is adjusted to (0), 2V, 4V, . . . ,
8V by sequentially turning on the switches in order of (each switch is in
an OFF state), SW1, SW2, . . . , SW4, or adjusted to 8V,
6V, . . . 2V, (0) by sequentially turning on the switches in order of
SW4, SW3, . . . SW1, (each switch is in the OFF state). In
other words, the output voltage is adjusted in increments of 2V. This
means that, if the number of switches is reduced, it becomes impossible
to finely adjust the output voltage in increments of a voltage across
each of the capacitors.

[0174] The present invention solves this problem by pulse width modulation
control (PWM control). Specifically, the preset invention makes it
possible to adjust a substantial output voltage as a meaning of a
temporal average value, in increments of a voltage across one capacitor,
in each of the electric energy storage apparatuses illustrated in FIGS.
2, 7, 12 and 13, even if a switch is provided for respective two of the
series-connected capacitors as in the electric energy storage apparatus
illustrated in FIG. 16. The method will be described based on an example
where the number of switches becomes half in the electric energy storage
apparatus illustrated in FIG. 2, i.e., based on an electric energy
storage apparatus 1 illustrated in FIG. 19 (this method may be
implemented in each of the electric energy storage apparatuses
illustrated in FIGS. 7, 12 and 13, according to the sample principle).

[0175] In this method, after completion of one cycle of the output voltage
adjustment based on the switch changeover in the switch group 4 and the
selection of the output terminals in the positive-negative inversion
circuit 5, as a part of the operation described in connection with the
first embodiment, etc., a high-speed changeover in a switch group 4 is
performed in a first half of a predetermined time before start of a next
cycle of the output voltage adjustment.

[0176] Typically, a step of turning off all of the switches, and a step of
re-turning on each of the switches which has been turned on in the
previous cycle of the output voltage adjustment, will be repeated plural
times, at a given time interval ratio therebetween.

[0177] Specifically, in cases where, in the electric energy storage
apparatus 1 illustrated in FIG. 19, the switches in the switch group 4
are sequentially turned on in order of (each switch is in the OFF state),
SW1, SW2, . . . , SW4, SW3, . . . , SW1, (each
switch is in OFF state) to output a voltage having the same waveform as
that in FIG. 17, a high-speed changeover is performed between a state in
which all of the switches are turned off and a state in which the switch
SW1 is turned on, in a first half of a time (predetermined time)
between turn-on of the switch SW1 and turn-on of the switch
SW2. In cases where each changeover is performed at even time
intervals, a temporal average voltage value in the first half of the
predetermined time is V, whereas a temporal average voltage value in a
second half of the predetermined time where the high-speed changeover is
not performed, is 2V. In other words, as compared to the case where the
high-speed changeover is not performed, the increments for adjustment of
the substantial voltage as meaning of a temporal average value can be
reduced to 1/2.

[0178] In the same manner, a high-speed changeover is performed between a
state in which all of the switches are turned off and a state in which
the switch SW2 is turned on, in a first half of a time
(predetermined time) between turn-on of the switch SW2 and turn-on
of the switch SW3. In cases where each changeover is performed at a
time interval ratio of 1:3, a temporal average voltage value in the first
half of the predetermined time is 3V, whereas a temporal average voltage
value in a second half of the predetermined time where the high-speed
changeover is not performed, is 4V. In other words, as compared to the
case where the high-speed changeover is not performed, the increments for
adjustment of the substantial voltage as meaning of a temporal average
value can be reduced to 1/2.

[0179] In the subsequent switch changeover, a high-speed changeover is
performed in the same manner, so that it becomes possible to
substantially reduce the increments for the adjustment to 1/2 so as to
finely adjust the output voltage. FIG. 18 illustrates a temporal voltage
change obtained when the above method is employed.

[0180] In the above high-speed changeover, the time interval ratio in each
changeover operation may be arbitrarily set. The increments for the
adjustment can be substantial adjusted to any rate other than 1/2 by
adjusting the time interval ratio to an arbitrary value.

[0181] In addition, it is not essential that the high-speed changeover is
performed, as discussed above, between the state in which all of the
switches are turned off and the state in which the switch which has been
selected in the output voltage adjustment is turned on. In other words, a
temporal average voltage value during the high-speed changeover can be
controlled to a desired value by selecting an arbitrary number of any
changeover states (without limiting the number to two), and arbitrarily
setting a time interval of each changeover. Further, it is not essential
that the high-speed changeover is performed in a front half of a
predetermined time.

SIXTH EXAMPLE

[0182] Each of the electric energy storage apparatuses according to the
first to fifth embodiments is configured to adjust voltages of the
respective capacitors, i.e., adjust the increments for adjustment of the
output voltage, by using the balancing circuit.

[0183] However, a constant-voltage DC power supply may be connected to
each of the capacitors to adjust voltages of the respective capacitors
without using the balancing circuit.

[0184] FIG. 20 and FIG. 21 illustrate two configurations formed by
connecting a constant-voltage DC power supply 28 to each of the
capacitors, instead of using the balancing circuit, respectively, in the
electric energy storage apparatuses 1 illustrated in FIG. 2 and FIG. 7.

[0185] Such the electric energy storage apparatuses 1 can also output a DC
or AC voltage according to the same principle as that in the first and
second embodiments, and may further comprise means for regeneratively
retuning excess energy according to the same principle as that in the
third and fifth embodiments. Further, the electric energy storage
apparatuses 1 may be used to finely adjust the output voltage as in the
fifth embodiment.

[0186] The electric energy storage apparatus 1 where a constant-voltage DC
power supply is connected to each of the capacitors is free of the need
for taking into account a voltage drop in each of the electric energy
storage modules due to discharging, so that it becomes possible to
simplify the control of the electric energy storage apparatus 1, as
comported to the first and second embodiment.

[0187] The electric energy storage apparatus of the present invention does
not use a DC-DC converter, an inverter or the like, so that it becomes
possible to output a voltage having an arbitrary pattern in a low-loss
and low-noise manner, irrespective of whether it is a DC voltage or an AC
voltage. Thus, the electric energy storage apparatus of the present
invention can be used as a highly-efficient power supply for any
electrically-operated device. The electric energy storage apparatus
employs, as a major element, a capacitor having a simple mechanism, and
therefor low in maintenance cost. Thus, also in view of the high
efficiency, it is suitable for use in the field of solar cells.

ADDITIONAL STATEMENT

[0188] As the aforementioned balancing circuit 2 for use in the electric
energy storage apparatus 1 of the present invention, a circuit comprising
an electric energy storage module disclosed in JP 2008-219964A (JP
2007-49692; JP 4352183B) may be used, as described in the embodiments
above. As one example of such a circuit, a circuit disclosed in FIG. 7 of
JP 2008-219964A will be described below.

[0189]FIG. 22 is a circuit diagram illustrating one embodiment of a cell
voltage equalization circuit disclosed in FIG. 7 of JP 2008-219964A. This
equalization circuit uses a secondary battery cell as an electric energy
storage cell, and has 3-series circuit configuration formed by connecting
3 series circuits in parallel, to have parallel rows consisting of
2-parallel row--3-parallel row--2-parallel row. Each of B1A to
B2A, B1B to B3B, and B2C to B3C, is a cell.
B1B and B3B is a cell having a capacity of 2X, and each of
the remaining cells has a capacity of X. Each of Sa1 to
Sa6 and Sb1 to SBb6 is a semiconductor switch. Two groups
of semiconductor switches, i.e., a Sa group and an Sb group,
are alternately turned on/off by using a driver, to change a combination
of cells to be connected in parallel in the module, so that the cells in
the module are subjected to mutual charging and discharging, to allow
voltages across the respective cells to be equalized. The on/off
operation using the driver may be performed in a constant cycle. Further,
the cycle may be changed depending on temporal change and/or load change.

[0190]FIG. 23 is a circuit diagram illustrating the equalization circuit,
wherein the switches in the Sa group are in an ON state, and the
switches in the Sb group are in an OFF state. In this mode,
B1A, B2B and B3C; B2A and B3B; and B1B and
B2C; are connected in parallel, respectively, to form a 3-series
circuit configuration formed by connecting 3 series circuits in parallel,
to have parallel rows consisting of 2-parallel row--3-parallel
row--2-parallel row. In this connection mode, a composite capacity in
each parallel row is equally 3X. Thus, if a variation in voltage
occurs between the parallel-connected cells, mutual charging and
discharging are performed, so that the voltage variation will move toward
being eliminated.

[0191]FIG. 24 is a circuit diagram illustrating the equalization circuit,
wherein the switches in the Sa group are in an OFF state, and the
switches in the Sb group are in an ON state. In this mode, B1A
and B1B; B2A, B2B and B2C; and B3B and B3C;
are connected in parallel, respectively, to form a 3-series circuit
configuration formed by connecting 3 series circuits in parallel, to have
parallel rows consisting of 2-parallel row--3-parallel row--2-parallel
row. In this connection mode, a composite capacity in each parallel row
is equally 3X. Thus, if a variation in voltage occurs between the
parallel-connected cells, mutual charging and discharging are performed,
so that the voltage variation will move toward being eliminated.

[0192] Based on repeating the above switch on/off operation, the
combination of series-connected and parallel-connected cells are changed
to allow each of the cells in the module to be connected in parallel with
each of the remaining cells, while maintaining a 3-series circuit
configuration formed by connecting 3 series circuits in parallel, to have
parallel rows consisting of 2-parallel row--3-parallel row--2-parallel
row, and maintaining a composite capacity in each parallel row equally
(3X), so that it becomes possible to perform mutual charging and
discharging between the parallel-connected cells to equalize voltages
across the respective cells.

[0193] The cell voltage equalization circuit in FIG. 22 is simply
illustrated by way of example, a similar balancing circuit may be formed
as a 4 or more-series circuit configuration and used in the electric
energy storage apparatus 1 of the present invention.

[0194] In one aspect, an electric energy storage apparatus is capable of
generating an AC output in a low-loss and low-noise manner without using
a DC-DC converter or an inverter. The electric energy storage apparatus
comprises: an electric energy storage module group formed by connecting
in series two or more electric energy storage modules each comprising one
or more electric energy storage elements; a balancing circuit
electrically connected to the electric energy storage module group and
configured to adjust a voltage to be applied to each of the electric
energy storage modules; a first switch group comprising two or more
switches each provided in a path connecting a first terminal and a
terminal of one of the series-connected electric energy storage modules;
and a second switch group comprising two or more switches each provided
in a path connecting a second terminal and a terminal of one of the
series-connected electric energy storage modules. The electric energy
storage apparatus is configured to perform a switch changeover in the
first and second switch groups so as to select a magnitude and polarity
of an output voltage depending on a configuration of the electric energy
storage elements present in a path connecting the first and second
terminals.

[0195] Although some embodiments of the invention have been shown and
described by way of example, it is obvious to those skilled in the art
that various changes and modifications may be made therein without
departing from the spirit and scope thereof as set forth in the appended
claims.